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Abstract:

A synthesizing unit of a receiving device according to an embodiment
synthesizes fixed components, which are fixed between carriers of an
effective symbol, included in inter-carrier interference (ICI) in a
broadcast signal on which fast Fourier transform (FFT) has been performed
in view of an adding position of the guard interval in the broadcast
signal and ICI in a broadcast signal on which FFT has been performed
without considering the adding position, according to an addition amount
of the guard interval. The ICI calculating unit calculates ICI to be
removed from the broadcast signal based on the fixed component
synthesized by the synthesizing unit.

Claims:

1. A receiving device, comprising: a receiving unit that receives a
broadcast signal in which a guard interval copied from a tail part of an
effective symbol including broadcast content is added to a head part of
the effective symbol; a guard adding unit that adds the guard interval
included in the broadcast signal received by the receiving unit to the
tail part of the broadcast signal; a fast Fourier transform (FFT) unit
that performs FFT on the broadcast signal to which the guard interval is
added; a synthesizing unit that synthesizes fixed components, which are
fixed between carriers of the effective symbol, included in inter-carrier
interference (ICI) in a broadcast signal on which FFT has been performed
in view of an adding position of the guard interval in the broadcast
signal and ICI in a broadcast signal on which FFT has been performed
without considering the adding position, according to an addition amount
of the guard interval; and an ICI calculating unit that calculates ICI to
be removed from the FFT-processed broadcast signal based on the fixed
component synthesized by the synthesizing unit.

2. The receiving device according to claim 1, wherein the ICI calculating
unit calculates a variation component, which changes for each carrier,
included in both of the ICI in the broadcast signal on which the FFT has
been performed in view of the adding position and the ICI in the
broadcast signal on which the FFT has been performed without considering
the adding position, and calculates the ICI based on the variation
component and the fixed component synthesized by the synthesizing unit.

3. The receiving device according to claim 1, further comprising, a
coefficient storage unit that stores a coefficient, which is common in
the fixed components, for each difference between a carrier number of the
effective symbol and a carrier number of an effective symbol that exerts
ICI over the effective symbol.

4. The receiving device according to claim 2, further comprising, a
coefficient storage unit that stores a coefficient, which is common in
the fixed components, for each difference between a carrier number of the
effective symbol and a carrier number of an effective symbol that exerts
ICI over the effective symbol.

5. A receiving method, comprising: receiving a broadcast signal in which
a guard interval copied from a tail part of an effective symbol including
broadcast content is added to a head part of the effective symbol; adding
the guard interval included in the received broadcast signal to a
corresponding tail part of the effective symbol in the broadcast signal;
performing fast Fourier transform (FFT) on the broadcast signal to which
the guard interval is added; synthesizing fixed components, which are
fixed between carriers of the effective symbol, included in inter-carrier
interference (ICI) in a broadcast signal on which FFT has been performed
in view of an adding position of the guard interval in the broadcast
signal and ICI in a broadcast signal on which FFT has been performed
without considering the adding position, according to an addition amount
of the guard interval; and calculating ICI to be removed from the
FFT-processed broadcast signal based on the fixed component synthesized
according to the addition amount of the guard interval.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2011-218293, filed on Sep. 30, 2011,
the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] An embodiment of the disclosure relates to a receiving device and a
receiving method.

[0004] 2. Description of the Related Art

[0005] In recent years, broadcast signals used in digital television
broadcasting conform to OFDM (Orthogonal Frequency Division Multiplexing)
scheme. The OFDM scheme is a technique of effectively transmitting data
using a limited frequency band by transmitting effective symbols
including broadcast content in a parallel way through a plurality of
carriers having phases orthogonal to each other.

[0006] A receiving device that receives a broadcast signal according to
the OFDM scheme acquires a symbol corresponding to data from the
broadcast signal by performing FFT (fast Fourier transform) on the
received broadcast signal, and reproduces broadcast content by performing
OFDM demodulation on the acquired symbol.

[0007] Meanwhile, a broadcasting station that transmits a broadcast signal
according to the OFDM scheme adds a guard interval copied from a tail
part of each effective symbol to a head part of each effective symbol and
then transmits each symbol in order to improve immunity to a multipath
delay.

[0008] As described above, the same data (symbol) as a part of an
effective symbol is included in the guard interval. Based on this, a
technique of improving a receiving characteristic by synthesizing the
guard interval with the effective symbol has been proposed.

[0009] For example, a receiving device disclosed in JP2000-151542A
improves a receiving characteristic by delaying a guard interval by a
time corresponding to the duration of an effective symbol and then
adding/synthesizing the guard interval to/with a tail part of an
effective symbol before performing FFT on a received broadcast signal.

[0010] Meanwhile, in a receiving device for a vehicle, when a broadcast
signal is received during high-speed movement, orthogonality of a carrier
collapses due to Doppler shift, causing inter-carrier interference. When
the inter-carrier interference occurs, it is difficult for the receiving
device to acquire a valid symbol, and thus a receiving characteristic
degrades.

[0011] For this reason, for example, a receiving device improves a
receiving characteristic by calculating the ICI based on a time variation
of a transmission channel response of a received broadcast signal and
then removing the ICI from the broadcast signal.

[0012] Specifically, the receiving device acquires an SP (scattered pilot)
signal from the broadcast signal which has been subjected to the FFT.
Then, based on the acquired SP signal, the receiving device estimates an
original transmission channel response of the broadcast signal and
estimates a time variation of the transmission channel response of the
received broadcast signal.

[0013] Then, the receiving device calculates the ICI based on a difference
between the estimated original transmission channel response of the
broadcast signal and the time variation of the actual transmission
channel response, and removes the calculated the ICI from the broadcast
signal, thereby improving the receiving characteristic.

[0014] However, when the technique (hereinafter, referred to as a "guard
adding technique") of adding/synthesizing the guard interval to/with the
effective symbol is used together with the technique of removing the ICI,
the calculation accuracy of the ICI is lowered.

[0015] Specifically, in the guard adding technique, when the guard
interval is synthesized with the effective symbol, the guard interval is
delayed by a time corresponding to the duration of the effective symbol
and then synthesized with the effective symbol before the FFT is
performed.

[0016] However, in the technique of removing the ICI, the ICI is
calculated based on the FFT-processed broadcast signal, and influence
caused by delaying the guard interval before the FFT is performed is
reflected in the time variation of the transmission channel response used
to calculate the ICI.

[0017] For this reason, when the guard adding technique is used together
with the technique of removing the ICI, it is difficult to accurately
calculate a time variation related to the transmission channel response
of the received broadcast signal, whereby the calculation accuracy of the
ICI is lowered.

[0018] Thus, how to implement a receiving device and a receiving method
which are capable of improving the calculation accuracy of the ICI while
using the guard adding technique together with the technique of removing
the ICI has become a big issue.

SUMMARY OF THE INVENTION

[0019] A receiving device according to an embodiment includes a receiving
unit, a guard adding unit, a FFT unit, a synthesizing unit, and an ICI
calculating unit. The receiving unit receives a broadcast signal in which
a guard interval copied from a tail part of an effective symbol including
broadcast content is added to a head part of the effective symbol. The
guard adding unit adds the guard interval included in the broadcast
signal received by the receiving unit to the tail part of the broadcast
signal. The FFT unit performs FFT on the broadcast signal to which the
guard interval is added. The synthesizing unit that synthesizes fixed
components, which are fixed between carriers of the effective symbol,
included in ICI in a broadcast signal on which FFT has been performed in
view of an adding position of the guard interval in the broadcast signal
and ICI in a broadcast signal on which FFT has been performed without
considering the adding position, according to an addition amount of the
guard interval. The ICI calculating unit calculates ICI to be removed
from the FFT-processed broadcast signal based on the fixed component
synthesized by the synthesizing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same becomes
better understood by reference to the following detailed description when
considered in connection with the accompanying drawings, wherein:

[0021]FIG. 1 is a schematic diagram illustrating a configuration of a
receiving device according to an embodiment;

[0022] FIGS. 2A and 2B are schematic diagrams illustrating a guard
addition process and an operation of an FFT unit according to an
embodiment; and

[0023]FIG. 3 is a schematic diagram illustrating a configuration of an
ICI removing unit according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of receiving device and a receiving
method disclosed in the present disclosure will be described in detail
with reference to the accompanying drawings. In the following, a
receiving device that receives a broadcast signal for digital television
broadcasting to which the OFDM (Orthogonal Frequency Division
Multiplexing) scheme is applied is described as an example of a receiving
device.

[0025]FIG. 1 is a schematic diagram illustrating a configuration of a
receiving device 1 according to an embodiment. FIG. 1 illustrates only
components necessary to describe a feature of the receiving device 1, and
general components are not illustrated.

[0026] The receiving device 1 illustrated in FIG. 1 is a device that
receives a broadcast signal including a duration of an effective symbol
containing broadcast content and a duration of a guard interval which is
copied from a tail part of the effective symbol and added to a head part
of the duration of the effective symbol. The receiving device 1 executes
predetermined signal processing on the received broadcast signal, and
outputs the signal-processed broadcast signal to be reproduced by an
output device such as a display device or a speaker (not illustrated).

[0029] The receiving unit 3 is a tuner that receives the broadcast signal
through the antenna 2 at a predetermined frequency band, and detects and
amplifies the received broadcast signal. The receiving unit 3 outputs the
detected and amplified analog broadcast signal Sig1 to the A/D converting
unit 4.

[0030] The A/D converting unit 4 is a processing unit that converts the
analog broadcast signal Sig1 input from the receiving unit 3 into a
digital broadcast signal Sig2, and outputs the digital broadcast signal
Sig2 to the guard adding unit 5. Here, the digital broadcast signal Sig2
output from the A/D converting unit 4 is the broadcast signal Sig2 in the
time domain.

[0031] The guard adding unit 5 is a processing unit that adds/synthesizes
a guard interval, which is included in the broadcast signal Sig2 input
from the A/D converting unit 4, to/with the tail part of the broadcast
signal. Sig2 which is the copy source of the guard interval. The guard
adding unit 5 outputs a broadcast signal Sig3 which has been subjected to
a guard addition process to the synchronizing unit 6 and the FFT unit 7.

[0032] Further, the guard adding unit 5 outputs a signal Sig4, which
represents an adding position (hereinafter, referred to as a "guard
adding position win") of the guard interval added to the tail part of the
broadcast signal Sig2 in the broadcast signal Sig1, to the ICI removing
unit 9.

[0033] In the following, the process of adding the guard interval through
the guard adding unit 5 is referred to as a "guard addition process." An
example of the guard addition process will be described later with
reference to FIGS. 2A and 2B together with a description of an operation
of the FFT unit 7.

[0034] The synchronizing unit 6 is a processing unit that performs symbol
synchronization of detecting a start position of the effective symbol in
the broadcast signal Sig3 which has been subjected to the guard addition
process, and outputs a signal Sig5 representing the detected position (a
delimiter between symbols in a data string) of the effective symbol to
the FFT unit 7. Further, the synchronizing unit 6 performs clock
synchronization of synchronizing a reference clock of a transmitting
device (not illustrated) that has transmitted the broadcast signal Sig3
with a reference clock of the receiving device 1.

[0035] The FFT unit 7 is a processing unit that performs the FFT on the
broadcast signal Sig3 input from the guard adding unit 5 based on the
signal Sig5 representing the start position of the effective symbol input
from the synchronizing unit 6, and transforms the broadcast signal Sig3
in the time domain into a broadcast signal Sig6 in the frequency domain.

[0036] Specifically, the FFT unit 7 performs the FFT on the broadcast
signal Sig3 input from the guard adding unit 5, and acquires a symbol (a
signal point) corresponding to data included in the broadcast signal
Sig3.

[0037] Then, the FFT unit 7 maps each acquired symbol of the broadcast
signal Sig3 with a receiving point in a constellation represented by an
in-phase component axis and a quadrature-component axis. Each symbol
mapped with the constellation is the broadcast signal Sig6 which has been
subjected to the FFT.

[0039] Here, the guard addition process performed by the guard adding unit
5 will be described with reference to FIGS. 2A and 2B together with a
description of an operation of the FFT unit 7. FIGS. 2A and 2B are
schematic diagrams illustrating operations of the guard addition process
and the FFT unit 7 according to an embodiment.

[0040] As illustrated in FIG. 2A, the FFT unit 7 receives the broadcast
signal Sig3, which has been subjected to the guard addition process, from
the guard adding unit 5. For example, the guard adding unit 5 generates
the broadcast signal Sig3 by the following processing.

[0041] Specifically, the guard adding unit 5 delays a guard interval G
added to a head part of an effective symbol. D by a time corresponding to
a duration length of the effective symbol D as indicated by a dashed
arrow in FIG. 2A.

[0042] Subsequently, the guard adding unit 5 performs the guard addition
process such that the effective symbol D is synthesized with the guard
interval G by adding the tail part of the effective symbol D before delay
to the delayed guard interval G.

[0043] In the above-described way, the guard adding unit 5 generates the
broadcast signal Sig3 that includes, for example, data of the copy source
of the guard interval G in the tail part of the effective symbol D and
data of the guard interval G by 50% as illustrated in FIG. 2A. The ratio
of the guard interval G, which is to be subjected to the guard addition
process, to the tail part of the effective symbol D is not limited to 50%
and can be appropriately changed.

[0044] As described above, the receiving device 1 performs the guard
addition process through the guard adding unit 5. Thus, when an error
occurs in the tail part of the received effective symbol D, data can be
complemented using the data of the guard interval G, so that the
receiving characteristic is improved.

[0045] Then, upon receiving the broadcast signal Sig3 which has been
subjected to the guard addition process, the FFT unit 7 performs the FFT
process on the effective symbol D part in the broadcast signal Sig3 (step
S1), and outputs the FFT-processed broadcast signal Sig6 to the
transmission channel calculating unit 8 and the ICI removing unit 9.

[0046] Here, the FFT-processed broadcast signal Sig3 is a signal in which
the data of the guard interval G occupies 50% in the tail part of the
effective symbol D as described above. Thus, the broadcast signal Sig3
can be regarded as a signal obtained by arithmetically averaging a
broadcast signal, to which the guard interval G is not added, illustrated
in the upper part of FIG. 2B and a broadcast signal, to which the guard
interval G is added, illustrated in the lower part of FIG. 2B.

[0047] Thus, the process of performing the FFT on the broadcast signal
Sig3 is equivalent to a process of performing the FFT on the broadcast
signal illustrated in the upper part of FIG. 2B (step S2), performing the
FFT on the broadcast signal illustrated in the lower part of FIG. 2B
(step S3), and arithmetically averaging broadcast signals Sig31 and Sig32
which have been subjected to the FFT (step S4).

[0048] An arithmetic process of performing the FFT on the broadcast signal
illustrated in the upper part of FIG. 2B is equivalent to an arithmetic
process of regarding the broadcast signal Sig3 as a signal which has not
been subjected to the guard addition process and thus performing the FFT
without considering the guard adding position win.

[0049] This arithmetic process can be expressed by a formula as follows.
Specifically, when the transmission channel response Sig7 of the
FFT-processed broadcast signal Sigh is assumed to change with respect to
the symbol time T of the effective symbol D in a linear function manner,
the broadcast signal illustrated in the upper part of FIG. 2B is
expressed by the following Expression (1).

[0059] When DFT (Discrete Fourier Transform) is performed on Expression
(1) to which m is assigned in order to perform the FFT on the above
signal, the DFT-processed broadcast signal Sig31 is expressed by the
following Expression (2).

[0062] Here, a first term in the last row of Expression (2) represents a
component that does not depend a time variation of the transmission
channel response Sig7 in the broadcast signal Sig31 which has been
subjected to the FFT (step S2), that is, a signal component including no
ICI. However, a second term in the last row of Expression (2) represents
ICI (hereinafter, referred to as "ICI1") which is caused by the time
variation of the transmission channel response Sig7 and included in the
broadcast signal Sig31.

[0063] Meanwhile, an arithmetic process of performing the FFT on the
broadcast signal illustrated in the lower part of FIG. 2B is equivalent
to an arithmetic process of regarding the broadcast signal Sig3 as a
signal which has been subjected to the guard addition process and thus
performing the FFT while considering the guard adding position win.

[0064] Specifically, the guard interval G in the broadcast signal
illustrated in the lower part of FIG. 2B is data which has been
originally added to the head part of the effective symbol D. In other
words, in the broadcast signal illustrated in the lower part of FIG. 2B,
the guard interval G is arranged at the position corresponding to a
reception time different from an original reception time.

[0065] For this reason, when the transmission channel response Sig7 of the
FFT-processed broadcast signal Sigh is assumed to change with respect to
the reception time T of the effective symbol in a linear function manner,
if the FFT is performed on the broadcast signal illustrated in the lower
part of FIG. 2B without considering the guard adding position win, an
error occurs in ICI.

[0066] In other words, when the FFT is performed on the broadcast signal
illustrated in the lower part of FIG. 2B without considering the guard
adding position win, the FFT is performed under determination that the
part of the guard interval G is received at a reception time different
from an actual reception time. As a result, ICI included in the
FFT-processed broadcast signal Sig32 becomes inaccurate ICI in which the
error of the reception time of the guard interval G is reflected.

[0067] Thus, when the FFT is performed on the broadcast signal illustrated
in the upper part of FIG. 2B, the reception time of the guard interval G,
that is, an arithmetic process of performing the FFT while considering
the guard adding position win representing the adding position of the
guard interval G in the broadcast signal Sig1 at the time of reception is
necessary.

[0068] This arithmetic process can be expressed by a formula as follows.
Specifically, when the transmission channel response Sig7 of the
FFT-processed broadcast signal Sig6 is assumed to change with respect to
the symbol time T of the effective symbol D in a linear function manner,
the broadcast signal to which the guard interval G illustrated in the
lower part of FIG. 2B is added is expressed by the following Expression
(3).

[0071] As described above, in Expression (3), the broadcast signal
illustrated in the lower part of FIG. 2B is classified by a time sample
number i in which the effective symbol D and the guard interval G is
received in view of the guard adding position win.

[0072] When the DFT is performed on Expression (3) to which m is assigned
in order to perform the FFT on the broadcast signal, the DFT-processed
broadcast signal Sig32 is expressed by the following Expression (4).

[0074] Here, a first term in the last row of Expression (5) represents a
signal component of the broadcast signal Sig31 that does not depend on
the time variation of the transmission channel response, that is, a
signal component including no ICI. A second term in the last row of
Expression (5) represents ICI (hereinafter, referred to as "ICI2") which
is caused by the time variation of the transmission channel response and
included in the broadcast signal Sig32.

[0075] For this reason, when the above-described arithmetic process is
performed, the FFT unit 7 outputs the broadcast signal Sig6 obtained by
arithmetically averaging the broadcast signal Sig31 and the broadcast
signal Sig32. In other words, the FFT unit 7 outputs the broadcast signal
Sigh including ICI1 and ICI2.

[0076] As described above, when the broadcast signal Sig6 includes ICI1
and ICI2, there occurs a problem in that the receiving characteristic is
lowered since it is difficult to acquire a valid symbol from each carrier
of the broadcast signal Sig6. In order to prevent the occurrence of the
problem, the receiving device 1 includes the ICI removing unit 9.

[0077] The ICI removing unit 9 is a processing unit that removes the ICI1
and ICI2 from the broadcast signal Sig6 input from the FFT unit 7, and
then outputs a broadcast signal Sig8 including no the ICI1 and ICI2 to
the equalization processing unit 10 (see FIG. 1).

[0078] Here, for example, ICI which has to be removed from the
FFT-processed broadcast signal Sig6 may be calculated such that the ICI
removing unit 9 calculates the ICI by individually calculating each of
the ICI1 and the ICI2 and arithmetically averaging the ICI1 and the ICI2
may be used as a method of calculating ICI.

[0079] In this way, by individually calculating the ICI1 and the ICI2 and
then arithmetically averaging the ICI1 and the ICI2, it is possible to
prevent influence caused by delaying the guard interval G at the time of
the guard addition process from being reflected in ICI.

[0080] Thus, when the ICI which has to be removed from the FFT-processed
broadcast signal Sigh is calculated by the above-mentioned method, the
calculation accuracy can be improved using the guard adding technique and
the technique of removing the ICI together.

[0081] Here, an example in which the ICI is calculated by individually
calculating the ICI1 and the ICI2 and arithmetically averaging the ICI1
and the ICI2 will be described in further detail. In this case, ICI1(m)
which a symbol of a carrier number n receives from a symbol of a carrier
number m is represented by Expression (6) based on the second term in the
last row of Expression (2).

[0082] Further, ICI2(m) which the symbol of the carrier number n receives
from the symbol of the carrier number m is represented by Expression (7)
based on the second term in the last row of Expression (5).

[0083] When the ICI1(m) and the ICI2(m) are individually calculated as
described above, the ICI removing unit 9 classifies the FFT-processed
broadcast signal Sigh into a broadcast signal Sig31 on which the FFT has
been performed without considering the guard adding position win and a
broadcast signal Sig32 on which the FFT has been performed in view of the
guard adding position win, and then performs processing.

[0084] In other words, the ICI removing unit 9 performs a calculation of
each of Expression (6) and Expression (7), and calculates an
arithmetically average of both calculation results as ICI to remove.
Through this operation, the ICI removing unit 9 can calculate ICI from
which an error caused by delaying the guard interval G at the time of the
guard addition process is excluded with a high degree of accuracy.

[0085] However, in the above-described configuration, as described above,
it is necessary to individually calculate the ICI1(m) and the ICI2(m).
Thus, in the above-described configuration, a circuit configuration of an
arithmetic circuit is complicated and so the circuit size increases, and
it is difficult to implement the ICI removing unit 9 of large scan
integration (LSI).

[0086] In this regard, in the present embodiment, the ICI removing unit 9
is configured to calculate the ICI which has to be removed from the
FFT-processed broadcast signal Sig6 without individually calculating the
ICI1(m) and the ICI2(m).

[0087] Here, the details of a calculation method of calculating the ICI
which has to be removed from the FFT-processed broadcast signal Sig6
without individually calculating the ICI1(m) and the ICI2(m) will be
described.

[0088] First, when Expression (6) for calculating the ICI1(m) is compared
with Expression (7) for calculating ICI2(m), both formulas have a common
variation component that changes for each carrier of the effective symbol
D and a non-common fixed component which is fixed between carriers.

[0089] Specifically, an in Expression (6) and Expression (7) is a
transmission signal of an n-th carrier, and is variation component that
changes depending on the carrier number n. Further, Δhn is a time
variation of a transmission channel response in the n-th carrier, and is
a variation component that changes depending on the carrier number n. N
is an integer representing the number of FFT stages. T is an integer
representing a symbol time (a time necessary to receive each symbol).

[0090] However, a function behind T in Expression (6) and Expression (7)
is a fixed component which is fixed for each difference between carrier
numbers, that is, between carriers. The ICI that has to be removed from
the FFT-processed broadcast signal Sig6 is a calculation result of
arithmetically averaging the ICI1(m) calculated by Expression (6) and the
ICI2(m) calculated by Expression (7).

[0091] Thus, using the variation component as a common term, a formula for
calculating the ICI that has to be removed from the FFT-processed
broadcast signal Sig6 is represented by the following Expression (8).

[0092] As described above, Expression (8) for calculating the ICI includes
the fixed component and the variation component. Thus, in the present
embodiment, a synthesizing unit that synthesizes the fixed components in
the ICI1(m) and the ICI2(m) according to an addition amount (hereinafter,
referred to as a "guard addition amount") of the guard interval G is
disposed in the ICI removing unit 9.

[0093] Further, in the present embodiment, the ICI removing unit 9 is
configured to calculate the ICI that has to be removed from the
FFT-processed broadcast signal based on the fixed component which is
common in the ICI1(m) and the ICI2(m) and the fixed component synthesized
by the synthesizing unit. Thus, the ICI removing unit 9 needs not to
individually calculate the ICI1(m) and ICI2(m).

[0094] Further, in the present embodiment, the guard addition amount
occupies 50% of the entire tail part of the FFT-processed broadcast
signal Sig6. For this reason, the ICI removing unit 9 performs the
synthesis by arithmetically averaging the fixed component in the ICI1(m)
and the fixed component in the ICI2(m). Then, the ICI removing unit 9
calculates the ICI by multiplying the synthesized fixed component by the
variation component which is common in the ICI1(m) and the ICI2(m).

[0095] As described above, the ICI removing unit 9 can calculate the ICI
that has to be removed from the FFT-processed broadcast signal Sigh by a
relatively simple and small arithmetic circuit that performs the
arithmetic process of Expression (8) without individually calculating the
ICI1(m) and the ICI2(m).

[0096] Next, a configuration of the ICI removing unit 9 that performs the
arithmetic process of Expression (8) and calculates the ICI that has to
be removed from the FFT-processed broadcast signal Sig6 will be described
with reference to FIG. 3. FIG. 3 is a schematic diagram illustrating a
configuration of the ICI removing unit 9 according to an embodiment.

[0098] The coefficient storage unit 90 is a storage unit that stores a
coefficient ζk (k=n-m) which is common in the fixed component
included in the ICI in the broadcast signal Sig31 FFT-processed without
considering the guard adding position win and the fixed component
included in the ICI in the broadcast signal Sig32 FFT-processed in view
of the guard adding position win.

[0099] Specifically, the coefficient storage unit 90 stores a coefficient
ζk (k=n-m=-10, -9, . . . 0, . . . 9, and 10) which is fixed
between carriers in Expression (8). Here, n in the coefficient
ζk is a carrier number of the effective symbol D which is an
ICI calculation target, and m is a carrier number of another effective
symbol D that exerts influence of ICI over the effective symbol D of the
carrier number n.

[0100] As described above, the coefficient storage unit 90 stores the
coefficient ζk for each difference between the carrier number n
and the carrier number m. Further, in order to reduce a calculation
amount in the ICI removing unit 9, the coefficient storage unit 90
according to the present embodiment stores 20 coefficients corresponding
to the difference between the carrier numbers n and m in view of the ICI
leaked from 10 carriers at the left and right (ahead of and behind) of
the carrier which is the ICI calculation target.

[0101] Upon receiving the signal Sig4 from the guard adding unit 5, the
multiplying unit 91 acquires information Sig12 corresponding to the
coefficient ζk from the coefficient storage unit 90, performs a
predetermined multiplication process, and outputs a multiplication result
Sig13 expressed by the following Expression (9) to the adding unit 92.

[ Expression 8 ] Sig 13 :
ζ k - j 2 π k win N ( 9
) ##EQU00009##

[0102] Upon receiving the multiplication result Sig13 from the multiplying
unit 91, the adding unit 92 acquires information Sig12 corresponding to
the coefficient from the coefficient storage unit 90, performs a
predetermined addition process, and outputs an addition result Sig14
expressed by the following Expression (10) to the amplifying unit 93.

[0103] Upon receiving the addition result Sig14 from the adding unit 92,
the amplifying unit 93 amplifies the addition result Sig14 0.5 times, and
outputs an amplification result Sig15 expressed by the following
Expression (11) to the ICI amount calculating unit 98.

[0104] As described above, the ICI removing unit 9 functions as the
synthesizing unit that synthesizes the fixed components fixed between
carriers in the ICI1 and ICI2 in cooperation with the coefficient storage
unit 90, the multiplying unit 91, the adding unit 92, and the amplifying
unit 93 according to the guard addition amount.

[0105] Upon receiving the transmission channel response Sig7 from the
transmission channel calculating unit 8, the transmission channel buffer
94 delays the transmission channel response Sig7 by a predetermined time,
and then outputs the delayed transmission channel response Sig16 to the
ICI amount calculating unit 98. Further, the transmission channel
response Sig7 which has not been delayed is input from the transmission
channel calculating unit 8 to the ICI amount calculating unit 98.

[0106] In the present embodiment, as an example, the ICI removing unit 9
is configured such that a transmission channel response Sig7 of an
immediately previous symbol and a transmission channel response Sig16 of
an immediately next symbol are input to the ICI amount calculating unit
98. Through this configuration, the ICI amount calculating unit 98 can
calculate the time variation Δhn of the transmission channel
response in Expression (7).

[0107] Upon receiving the FFT-processed broadcast signal Sigh from the FFT
unit 7, the equalization processing unit 95 performs waveform
equalization on the broadcast signal Sig6, and outputs a broadcast signal
Sig17 which has been subjected to the waveform equalization to the
tentative determining unit 96.

[0108] The equalization processing unit 95 performs waveform equalization
such that the phase and amplitude of the SP signal, at the time of
transmission, which is included in the broadcast signal Sig6 are
reconstructed by multiplying the broadcast signal Sig6 input from the FFT
unit 7 by a reverse characteristic of the transmission channel response
Sig7 input from the transmission channel calculating unit 8.

[0109] Upon receiving the broadcast signal. Sig17, which has been
subjected to the waveform equalization, from the equalization processing
unit 95, the tentative determining unit 96 estimates the transmission
signal an which is the broadcast signal Sig17 at the time of
transmission by tentatively determining the broadcast signal Sig17 based
on the difference between the SP signal before the waveform equalization
and the SP signal after the waveform equalization. Then, the tentative
determining unit 96 outputs a broadcast signal Sig18 corresponding to the
estimated transmission signal an to the ICI amount calculating unit
98.

[0110] The ICI amount calculating unit 98 assigns the amplification result
Sig15 (see Expression 11), the time variation Δhn of the
transmission channel response, the broadcast signal Sig18 corresponding
to the transmission signal an to Expression (7), calculates the ICI
that has to be removed from the FFT-processed broadcast signal Sig6, and
outputs the ICI to the subtracting unit 99.

[0111] Upon receiving the FFT-processed broadcast signal Sig6 from the FFT
unit 7, the data buffer 97 delays the broadcast signal Sig6 by a
predetermined time, and outputs the delayed broadcast signal Sig19 to the
subtracting unit 99.

[0112] Here, the data buffer 97 outputs a broadcast signal Sig19, which is
obtained by delaying the broadcast signal Sig6 by a time from when the
signal Sig4 representing the guard adding position win is input to the
multiplying unit 91 to when the amplifying unit 93 outputs the
amplification result Sig15, to the subtracting unit 99.

[0113] As a result, the broadcast signal Sig19 and the ICI amount which
correspond to the same symbol received at the same time are input from
the data buffer 97 and the ICI amount calculating unit 98 to the
subtracting unit 99, respectively.

[0114] The subtracting unit 99 generates the broadcast signal Sig8 from
which the ICI is removed by subtracting the ICI input by the ICI amount
calculating unit 98 from the broadcast signal Sig19 input by the data
buffer 97, and then outputs the generated broadcast signal Sig8 to the
equalization processing unit 10.

[0115] As described above, the ICI removing unit 9 synthesizes the fixed
components fixed between carriers in the ICI1 and the ICI2 according to
the guard addition amount, and calculates the ICI that has to be removed
from the FFT-processed broadcast signal based on the synthesized fixed
component.

[0116] Here, returning to FIG. 1, the description of the receiving device
1 continues. The broadcast signal Sig8 from which the ICI has been
removed by the ICI removing unit 9 is input to the equalization
processing unit 10. Further, the transmission channel response Sig7 is
input from the transmission channel calculating unit 8 to the
equalization processing unit 10.

[0117] The equalization processing unit 10 is a processing unit that
performs the same equalization process as in the equalization processing
unit 95 illustrated in FIG. 3 on the broadcast signal Sig8, from which
the ICI is removed, input from the ICI removing unit 9 using the
transmission channel response Sig7 input from the transmission channel
calculating unit 8. The equalization processing unit 10 outputs the
broadcast signal Sig9, which has been subjected to the equalization
process, to the tentative determination likelihood calculating unit 11.

[0118] The tentative determination likelihood calculating unit 11 is a
processing unit that performs the same tentative determination as in the
tentative determining unit 96 illustrated in FIG. 3 on the broadcast
signal Sig9, which has been subjected to the equalization process, input
from the equalization processing unit 10, and calculates the likelihood
of the tentatively determined broadcast signal. The tentative
determination likelihood calculating unit 11 outputs the tentatively
determined broadcast signal Sig10 including the calculated likelihood to
the error correction TS output unit 12.

[0119] The error correction TS output unit 12 is a processing unit that
performs a well-known error correction process on the broadcast signal
Sig10 using the likelihood included in the tentatively determined
broadcast signal Sig10 input from the tentative determination likelihood
calculating unit 11, a convolutional code, a Reed-Solomon code, and the
like. The error correction. TS output unit 12 outputs an error-corrected
TS signal Sig11 to be reproduced through an output reproduction device
(not illustrated) such as a display or a speaker.

[0120] As described above, the receiving device 1 according to the present
embodiment includes the receiving unit 3, the guard adding unit 5, the
FFT unit 7, the synthesizing unit, and the ICI amount calculating unit
98. The receiving unit 3 receives the broadcast signal in which the guard
interval G copied from the tail part of the effective symbol D including
broadcast content is added to the head part of the effective symbol D.

[0121] The guard adding unit 5 adds the guard interval G included in the
broadcast signal received by the receiving unit 3 to the tail part of the
broadcast signal. The FFT unit 7 performs the FFT on the broadcast signal
Sig3 to which the guard interval G is added.

[0122] The synthesizing unit synthesizes the fixed components, which are
fixed between carriers of the effective symbol D, included in the ICI in
the broadcast signal Sig32 on which the FFT has been performed in view of
the adding position (the guard adding position win) of the guard interval
G in the broadcast signal. Sig1 and the ICI in the broadcast signal.
Sig31 on which the FFT has been performed without considering the adding
position (the guard adding position win), according to the addition
amount of the guard interval G.

[0123] Then, the ICI amount calculating unit 98 calculates the ICI to be
removed from the FFT-processed broadcast signal Sig6 based on the fixed
component synthesized by the synthesizing unit.

[0124] Through the above-described operation, the receiving device 1 can
prevent influence caused by delaying the guard interval G at the time of
the guard addition process from being reflected in the ICI, and thus can
calculate the ICI that has to be removed from the FFT-processed broadcast
signal Sigh with a high degree of accuracy. Thus, the receiving device 1
can improve the ICI calculation accuracy using the guard adding technique
and the technique of removing the ICI together.

[0125] Further, in the receiving device 1, the ICI amount calculating unit
98 calculates the variation component, which changes for each carrier of
the effective symbol D, included in both of the ICI in the broadcast
signal Sig32 on which the FFT has been performed in view of the guard
adding position win in the broadcast signal Sig1 and the ICI in the
broadcast signal. Sig31 on which the FFT has been performed without
considering the guard adding position win.

[0126] Then, the ICI amount calculating unit 98 calculates the ICI that
has to be removed from the FFT-processed broadcast signal Sig6 based on
the calculated variation component and the fixed component synthesized by
the synthesizing unit. In other words, the receiving device 1 can
calculate the ICI that has to be removed from the FFT-processed broadcast
signal Sig6 without individually calculating the ICI1 in the broadcast
signal Sig32 on which the FFT has been performed in view of the guard
adding position win and the ICI 2 in the broadcast signal Sig31 on which
the FFT has been performed without considering the guard adding position
win.

[0127] Through this operation, the receiving device 1 can simplify the
circuit configuration of the ICI amount calculating unit 98 and reduce
the circuit size, and thus easily implement the receiving device 1 of
LSI.

[0128] Further, in the receiving device 1, the ICI removing unit 9
includes the coefficient storage unit 90 that stores a coefficient
ζk which is common in the fixed component included in the ICI
in the broadcast signal Sig31 FFT-processed without considering the guard
adding position win and the fixed component included in the ICI in the
broadcast signal Sig32 FFT-processed in view of the guard adding position
win in the broadcast signal Sig1.

[0129] Further, the coefficient storage unit 90 stores the coefficient
ζk for each difference (n-m) between the carrier number of the
effective symbol D and the carrier number of another effective symbol D
that exerts influence of ICI over the effective symbol D.

[0130] Through this operation, the receiving device 1 can reduce a
processing time necessary to calculate the ICI since it is unnecessary to
calculate coefficient ζk each time the ICI that has to be
removed from the FFT-processed broadcast signal. Sig6 is calculated.

[0131] The above embodiment has been described in connection with the
example in which the guard adding unit 5 generates the broadcast signal
Sig3 in which each of the data of the copy source of the guard interval G
and the data of the guard interval G occupies 50% of the tail part of the
effective symbol D, but this is merely an example.

[0132] In other words, the guard adding unit 5 may be configured to add
the guard interval G of an arbitrary addition amount to the tail part of
the effective symbol D. In this configuration, the ICI removing unit 9 is
configured to synthesize the fixed component in the ICI1 with the fixed
component in the ICI2 at a synthesis rate corresponding to the addition
amount of the added guard interval G.

[0133] For example, the description will proceed with an example in which
the guard adding unit 5 generates the broadcast signal Sig3 in which the
ratio of the data of the copy source of the guard interval G and the data
of the guard interval G in the tail part of the effective symbol D is 6
to 4.

[0134] In this case, in the ICI removing unit 9, the configuration of the
synthesizing unit is changed to generate the amplification result Sig15
that includes the fixed component in the ICI1 and the fixed component in
the ICI2 by 60% and 40%, respectively.

[0135] As described above, when the addition amount of the guard interval
G added to the tail part of the effective symbol D is changed, by
changing the configuration of the synthesizing unit, the receiving device
1 can calculate the ICI that has to be removed from the FFT-processed
broadcast signal Sigh with a high degree of accuracy.

[0136] Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects is
not limited to the specific details and representative embodiments shown
and described herein. Accordingly, various modifications may be made
without departing from the spirit or scope of the general inventive
concept as defined by the appended claims and their equivalents.

Patent applications by FUJITSU TEN LIMITED

Patent applications in class Particular pulse demodulator or detector

Patent applications in all subclasses Particular pulse demodulator or detector